Polymeric films such as cellophane, oriented polypropylene, blown polyethylene, polyvinyl chloride (PVC), and a multitude of others which comprise polymers of low surface energy, have been used for decades in the packaging of a wide variety of goods. These films are characterized by high resistance to moisture vapor transmission, making them desirable in the packaging of moist products, such as meats, vegetables, prepared food products, etc., because the moisture content of the food is substantially retained in the package. Another desirable property of the films is their transparency, enabling the visual identification of the food products packaged within. However, when saturating water evaporates from moist food, it may saturate the air spaces between the film and the food and begin condensing on the inner surface of the film as minute droplets of water. As more condensation or water droplets form on the film, an overall fogged effect is observed, interfering with the see-through quality of the film.
In order to prevent water from condensing in droplets, an antifog agent is often added to the film. The antifog agents raise the surface energy of the film and/or reduce the surface tension of the water and cause the water to form a continuous sheet, which is then transparent. A great number of antifog agents have been suggested as additives to films, for example various glyceryl esters of fatty acids have been disclosed in U.S. Pat. No. 3,048,263 as antifogging agents for polyolefin films in an amount between 0.5 percent to 1 percent by weight. U.S. Pat. No. 4,835,194 discloses the use of certain ethoxylated nonyl- or decylphenols in linear ethylene polymers. U.S. Pat. No. 4,486,552 discloses an anti-fog blend of glyceryl esters, alkoxylated alkylphenols, and polyalkoxylated fatty acid esters. The prior art antifog agents all take some time before they take effect and become noticeable.
There is a perceived need in the market place for polymeric films with improved fog-resistant properties.